Multiple heatsink cooling system for a line voltage thermostat

ABSTRACT

A line voltage thermostat having a multiple heatsink switch. A total switch may have a semiconductor switch mounted on each heatsink of the multiple heatsink switch. The semiconductor switches of the respective heatsinks may be connected in parallel to represent the total switch. Each of the two or more heatsinks, having a semiconductor switch for switching, and in total conveying the same power as one equivalent switch with one total heatsink, may have higher maximum operating temperatures and higher thermal resistances than twice the thermal resistance of the one total heatsink. The two or more heatsinks may be situated within a housing of the line voltage thermostat, and be easier to distribute in the housing to achieve an efficient layout of a display and control buttons for the thermostat.

BACKGROUND

The present disclosure pertains to switches and particularly toheatsinks associated with the switches. More particularly, thedisclosure pertains to switches for thermostats.

SUMMARY

The disclosure reveals a line voltage thermostat having a multipleheatsink switch. A total switch may have a semiconductor switch mountedon each heatsink of the multiple heatsink switch. The semiconductorswitches of the respective heatsinks may be connected in parallel torepresent the total switch. Each of the two or more heatsinks, having asemiconductor switch for switching, and in total conveying the samepower as one equivalent switch with one total heatsink, may have highermaximum operating temperatures and higher thermal resistances than twicethe thermal resistance of the one total heatsink. The two or moreheatsinks may be situated within a housing of the line voltagethermostat, and be easier to distribute in the housing to achieve anefficient layout of a display and control buttons for the thermostat.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram of an illustrative thermostat, a power source and anelectric load;

FIG. 2 is a diagram of thermal conductivity of an example triacarrangement;

FIG. 3 is a diagram that illustrates a two-heatsink principle with anexample layout of two SCR/triac and respective heatsink assemblies

FIG. 4a is a diagram of layout of a housing design that indicates anintegration of the double SCR/triac arrangement in a product rather thana single triac arrangement;

FIG. 4b is a diagram of some layouts of a housing design;

FIG. 5 is a diagram of housings of a commercial thermostat and a twoheatsink configuration for illustrating a size, display and layoutcomparison; and

FIG. 6 is a diagram of a graph that shows a non-linear relationshipbetween mass and thermal resistance for various models of thermostats.

DESCRIPTION

The present system and approach may incorporate one or more processors,computers, controllers, user interfaces, wireless and/or wireconnections, and/or the like, in an implementation described and/orshown herein.

This description may provide one or more illustrative and specificexamples or ways of implementing the present system and approach. Theremay be numerous other examples or ways of implementing the system andapproach.

Line voltage thermostats may be used to direct control of an electricalheater. High electrical power going through the switching component inthe thermostat produces excessive heat that may damage the componentitself. A single heatsink may be traditionally used in order to cooldown the switching component.

Often, a heat sink may take up to two-thirds of a thermostat envelopeand create many integration constraints. Such thermostat arrangement mayhave a bulky size, a limited screen size, limited positions of thescreen due to a heat source location, and limited positions for buttonlocations.

The present arrangement may incorporate two separate switchingcomponents such as triacs or SCRs (e.g., thyristors) and have eachcomponent installed with its own heat sink in the envelope. Thearrangement may permit each switching component to run at a higher tabtemperature since it has half of the original power going through itwhile having the same junction temperature as the single componentarrangement. The arrangement may incorporate more than two componentsand corresponding heat sinks.

The thermal performance of a heat sink may be a nonlinear function ofthe heat sink's overall size. Heat sinks of smaller size may be moreefficient.

In order for the present arrangement operate at its best in an envelope,both heat sinks should be the furthest apart from each other. Advantagesof the present arrangement compared to a single switching componentenvelope, for instance that of a thermostat, may incorporate a smalleroverall product and better aesthetics, or (if envelope size is keptconstant) a higher power rating. The arrangement may result in a betterintegration of screen such as a more favorable centering the screen andyet keeping it far from a heat source, a possibility of larger screen,and a centering of the buttons.

The present arrangement may be used to improve the aesthetics of aproduct such as the thermostat by reducing its size or increasing itspower rating without reducing its size. The arrangement may provide moreflexibility for human machine interface components integration such as ascreen and buttons. A new thermostat look and/or higher power rating maycreate a significantly competitive advantage in the market.

RF/heatsink compatibility (RF mechanical specifications) and RF maximumtemperature requirements (RF thermal specifications) may be aconsideration with the present arrangement. A printed circuit board(PCB) thermal model may incorporate dissipated power from otherelectronic components other than the triac, thermal resistance of thepower traces, a position of a compensation sensor, and ambient sensorthermal cooling and position.

Factors of concern may incorporate sizes and positions of electroniccomponents, a position of compensation sensor, ambient sensor thermalcooling and position, high temperature LCD and backlight, andthermopheresis (black soot deposition).

FIG. 1 is a diagram of an illustrative thermostat 71, a power supply orsource 72 and an electric load 73. Thermostat 71 may incorporate atemperature setpoint mechanism or device 74, a device, microcontrolleror mechanism 75 having a comparator function, and a power switch 76. Thecomparator function may be performed by an electronic or mechanicaldevice, mechanism, or by a microcontroller. Thermostat 71 may beconnected to a temperature sensor 77. Temperature sensor 77 may be inthermostat 71 or remote from thermostat 71. Power supply 72 may beconnected to a power switch or switching component 76 of thermostat 71.An electric load 73 may be connected to power switch 76 and power supply72. Electric load 73 may be a heater. Temperature sensor 77 and electricload 73 may be situated in the same area or space. Temperatureindications from temperature setpoint device 74 and temperature sensor77 may go to comparator function of a mechanism 75. Mechanism 75 with acomparator function may determine from the indications whether powerswitch 76 should be closed or not, relative to connecting electric loador heater 73 to power supply 72.

Power in a room may be controlled by a duty cycle on the full power tothe electric load or heater 73: time on/(time on+time off). For example,7.5 seconds on and 7.5 seconds off every 15 seconds on a 1000 Wbaseboard heater may be 50 percent of 1000 W=500 W of power delivered.

Thermostat 71 may also incorporate additional electronics and interfacecomponents 78 that may be connected with one or more components insideand outside of the diagram in FIG. 1. Electronics and interfacecomponents 78 may provide various functions of calculation, processingand power control of thermostat system 71.

FIG. 2 is a diagram of a thermal conductivity of an example triacarrangement 11. A triac 12 may be connected to the ambient air 14 viawires, PCB and thermostat structure, and represented by the thermalresistance 13 (Rwires). The other side of triac 12 may be connected tothe ambient air 14 via a flat surface heatsink 18 with a conductiveadhesive or other material 19, and represented by the thermal resistance16 (Rhs).

FIG. 3 is a diagram that illustrates a two-heatsink principle with anexample layout of two SCR/triac and respective heatsink assemblies 31and 32. An approximation or equivalent of the SCR assemblies may beshown in terms of one triac assembly 33. For the same total “q” (energy)of assemblies 31 and 32 together being the same for the single triacassembly 33, the thermal resistance of the junction the triac (Rjc),heatsink (Rhs), and connecting wires (Rwires) may be about one-half forassembly 33 of that for an SCR assembly.

Advantages of a two or more SCR/triac arrangement may incorporate thateach SCR/triac may operate at a higher temperature and its heatsink maybe smaller than a single triac arrangement. For instance, the triacmaximum tab temperature may be indicated by the formulaTj−Rjc*P=104−0.97*17.5=87° C. The double triac/SCRs maximum tabtemperature may be indicated by the formula Tj−Rjc*P=104−1*17.5/2=95° C.A smaller heatsink of a SCR or triac of a double arrangement may equateto a higher thermal resistance heatsink than twice the thermalresistance of a single triac.

Heatsink thermal resistance for a triac may be indicated by the formulaRth=(Tc−Ta)/P=(87−25)/17.5=3.54° C./W; twice that value is 7.08° C./W.The mass for the triac arrangement may be 90 g. Heatsink thermalresistance for a double triac/SCR arrangement may be indicated by theformula Rth=(Tc−Ta)/P=(95−25)/8.75=8° C./W. The mass for the doublearrangement may be 30 g; twice that value is 60 g.

FIG. 4a is a diagram of layout 41 of a housing 46 design that mayindicate a better integration of the double SCR/triac arrangement in aproduct than a single triac arrangement. FIG. 4b is a diagram of layouts42 and 43 of housing design 46. A placement of the two SCR/triac andheatsink assemblies 31 and 32 are revealed in layouts 41 and 43.Advantages of the design may incorporate a centered LCD 45 as shown inlayouts 41 and 42. Display 45 may instead be of a non-LCD technology.Display 45 may have dimensions of 24 mm×48 mm. Other dimensions ofcomponents in housing 46 may incorporate a PCB area of 8500 mm² (forcomparison, see a Honeywell TH104 PCB=5100 mm²), with no wall platerequired (a cost saving), a slim structure with a vertical concept (34mm), straight fins, and a 50 percent aluminum weight reduction, ascompared with the OEM637 noted herein.

FIG. 5 is a diagram of housings of a Honeywell TH104 thermostat 51 and atwo heatsink configuration for illustrating a size, display and layoutcomparison.

FIG. 6 is a diagram of a graph 61 that shows a non-linear relationshipbetween mass and thermal resistance for various models of thermostats.Point 62 represents the calculation for the triac and point 63represents the calculation for each SCR noted herein.

To recap, a thermostat for controlling an electric heater mayincorporate an ambient temperature sensor, a temperature setpointdevice, a comparator mechanism connected to the ambient temperaturesensor and the temperature setpoint device, and a power switch having acontrol terminal connected to the comparator mechanism. The power switchmay incorporate two or more separate heatsinks and a solid state switchsituated on each heatsink. Each solid state switch may have a controlinput connected to the control terminal of the power switch.

The thermostat may further incorporate a housing. The temperaturesetpoint device, the comparator mechanism and the power switch may besituated in the housing.

The ambient temperature sensor may be for indicating a temperature of aspace containing an electric heater connected to the power switch, andfor providing an output signal to the control terminal of the powerswitch or no output signal to the control terminal of the power switch.

The comparator mechanism may compare a first temperature indication fromthe ambient temperature sensor and a second temperature indication fromthe temperature setpoint device and provide a first output signal, asecond output signal or no output signal to the control terminal of thepower switch. The first output signal may indicate that the secondtemperature indication is X degrees greater than the first temperatureindication. The second output signal may indicate that the firsttemperature indication is Y degrees greater than the second temperatureindication. X may be a predetermined number. Y may be a predeterminednumber.

The first output signal may turn on the power switch. The second outputsignal may turn off the power switch. When the power switch is turnedoff, the electric heater may be disconnected from electric power. Whenthe power switch is turned on, the electric heater may be connected toelectric power.

The solid state switch may be selected from a group consisting of an SCRand a triac.

Each heatsink and corresponding solid state switch may be placed in thehousing at a distance from any other heatsink. The distance may be setat a maximum within the housing.

An approach, for controlling an electric load, may incorporate providinga thermostat having a power switch connectable to an electric load,determining how much power is to be delivered by an electric load,designating an amount of time the electric load is to be powered, anddesigning a power switch capable of turning on and off the power of anelectric load, having two or more solid state switches connected inparallel and attached to separate heatsinks. Each of the two or moresolid state switches may be capable of turning on and off the power ofthe electric load.

The approach may further incorporate measuring a temperature of a spacehaving a temperature to be controlled, selecting a desired temperatureto be provided to the space, and connecting the electric load to powerwith the power switch if the temperature of the space is less than thedesired temperature. The electric load may provide heat in the space toraise the temperature in the space when the electric load is connectedto the power.

The measuring the temperature in the space, selecting the desiredtemperature, and providing a signal to the power switch to connect theelectric load to power may be performed by a temperature sensor, atemperature setpoint device, and a comparator mechanism, respectively.

The temperature setpoint device, the comparator mechanism and the powerswitch may be contained within a housing. The housing may have athermostat that incorporates the temperature sensor, the temperaturesetpoint device, and the comparator mechanism.

A heatsink cooling system for a line voltage thermostat may incorporatea switching component and a thermostatic control. The switchingcomponent may incorporate two or more heatsinks, and a semiconductorswitch situated on each of the two or more heatsinks. Each semiconductorswitch may have an input connectable to a line voltage and an outputconnectable to an electric load, and have a control terminal. Thethermostatic control may have an output connected to the controlterminal of each semiconductor switch.

The thermostatic control may incorporate a housing, a temperaturesensor, a temperature setpoint mechanism, and an electronics moduleconnected to the temperature sensor, the temperature setpoint mechanism,and the output of the thermostatic control.

The temperature setpoint mechanism may be accessible on the housing orbe remote from the housing. The electronic module may be situated in thehousing. The switching component may be situated in the housing.

The two or more heatsinks may be situated in the housing at a maximumdistance from one another within the housing.

Increasing a number of heatsinks with the switching component having asemiconductor switch situated on each heatsink of a number of heatsinksgreater than one, may increase a maximum operating tab temperature foreach semiconductor switch and result in each of the more than oneheatsinks having a thermal resistance greater than a heatsink of aswitching component if the switching component has a total of onesemiconductor switch situated on just one heatsink for the same amountelectric load carried by the switching component having two or moresemiconductor switches with each semiconductor switch having at leastone heatsink. The semiconductor switch may be selected from a groupconsisting of a SCR and a triac.

The electric load may incorporate an electric heater in a space having atemperature that can be measured by the temperature sensor.

The mass of the two or more heatsinks of the switching component havingtwo or more semiconductor switches may be less than the mass of aheatsink of the switching component having just one semiconductor switchon one heatsink for the same electrical load.

In the present specification, some of the matter may be of ahypothetical or prophetic nature although stated in another manner ortense.

Although the present system and/or approach has been described withrespect to at least one illustrative example, many variations andmodifications will become apparent to those skilled in the art uponreading the specification. It is therefore the intention that theappended claims be interpreted as broadly as possible in view of therelated art to include all such variations and modifications.

What is claimed is:
 1. A thermostat for controlling an electric heatercomprising: an ambient temperature sensor; a temperature setpointdevice; a comparator mechanism connected to the ambient temperaturesensor and the temperature setpoint device; a power switch having acontrol terminal connected to the comparator mechanism; and wherein thepower switch comprises: two or more separate heatsinks; a solid stateswitch situated on each heatsink; and wherein each solid state switchhas a control input connected in parallel to the other solid stateswitches to the control terminal of the power switch to form the powerswitch; and wherein: the comparator mechanism compares a firsttemperature indication from the ambient temperature sensor and a secondtemperature indication from the temperature setpoint device and providesa first output signal, a second output signal or no output signal to thecontrol terminal of the power switch; the first output signal indicatesthat the second temperature indication is X degrees greater than thefirst temperature indication; the second output signal indicates thatthe first temperature indication is Y degrees greater than the secondtemperature indication; X is a predetermined number; and Y is apredetermined number.
 2. The thermostat of claim 1, further comprising:a housing; and wherein the temperature setpoint device, the comparatormechanism and the power switch are situated in the housing.
 3. Thethermostat of claim 1, wherein the ambient temperature sensor is forindicating a temperature of a space containing an electric heaterconnected to the power switch, and for providing an output signal to thecontrol terminal of the power switch or no output signal to the controlterminal of the power switch.
 4. The thermostat of claim 3, wherein: thefirst output signal turns on the power switch; and the second outputsignal turns off the power switch.
 5. The thermostat of claim 3,wherein: when the power switch is turned off, the electric heater isdisconnected from electric power; and when the power switch is turnedon, the electric heater is connected to electric power.
 6. Thethermostat of claim 1, wherein the solid state switch is selected from agroup consisting of an SCR and a triac.
 7. The thermostat of claim 2,wherein: each heatsink and a corresponding solid state switch are placedin the housing at a distance from any other heatsink; and the distanceis set at a maximum within the housing.
 8. A method, for controlling anelectric load, comprising: providing a thermostat comprising a powerswitch connectable to an electric load; determining how much power is tobe delivered by an electric load; designating an amount of time theelectric load is to be powered; and designing a power switch capable ofturning on and off the power of an electric load, incorporating two ormore solid state switches connected in parallel to form the power switchand attached to separate heatsinks; measuring a first temperature of aspace having a temperature to be controlled; and comparing a firsttemperature and a second temperature indication from the thermostat;providing a first output signal indicating that the second temperatureindication is X degrees greater than the first temperature, a secondoutput signal that indicated that the first temperature is Y degreesgreater than the second temperature indication, or no output signal tothe power switch; and wherein each of the two or more solid stateswitches is capable of turning on and off the power of the electricload.
 9. The method of claim 8, further comprising: connecting theelectric load to power with the power switch if the temperature of thespace is less than the desired temperature in response to the firstoutput signal; and wherein the electric load provides heat in the spaceto raise the temperature in the space when the electric load isconnected to the power.
 10. The method of claim 9, wherein the measuringthe temperature in the space, selecting the desired temperature, andproviding a signal to the power switch to connect the electric load topower are performed by a temperature sensor, a temperature setpointdevice, and a comparator mechanism, respectively.
 11. The method ofclaim 10, wherein the temperature setpoint device, the comparatormechanism and the power switch are contained within a housing.
 12. Themethod of claim 11, wherein the housing incorporates a thermostat thatcomprises the temperature sensor, the temperature setpoint device, andthe comparator mechanism.
 13. A heatsink cooling system for a linevoltage thermostat comprising: a switching component; and a thermostaticcontrol; a comparator mechanism; and wherein: the switching componentcomprises: two or more heatsinks; and a semiconductor switch situated oneach of the two or more heatsinks; and wherein each semiconductor switchhas an input connectable to a line voltage and an output connectable toan electric load, and has a control terminal; and the thermostaticcontrol has an output connected to the control terminal of eachsemiconductor switch; the comparator mechanism compares a firsttemperature indication from an ambient temperature sensor and a secondtemperature indication from the thermostatic control and provides afirst output signal, a second output signal or no output signal to thecontrol terminal of the switching component; the first output signalindicates that the second temperature indication is X degrees greaterthan the first temperature indication; the second output signalindicates that the first temperature indication is Y degrees greaterthan the second temperature indication.
 14. The system of claim 13,wherein the thermostatic control comprises: a housing; a temperaturesetpoint mechanism; and an electronics module connected to the ambienttemperature sensor, the temperature setpoint mechanism, and the outputof the thermostatic control.
 15. The system of claim 14, wherein: thetemperature setpoint mechanism is accessible on the housing or is remotefrom the housing; the electronic module is situated in the housing; andthe switching component is situated in the housing.
 16. The system ofclaim 15, wherein the two or more heatsinks are situated in the housingat a maximum distance from one another within the housing.
 17. Thesystem of claim 14, wherein the electric load comprises an electricheater in a space having a temperature that can be measured by thetemperature sensor.
 18. The system of claim 13, wherein thesemiconductor switch is selected from a group consisting of a SCR and atriac.
 19. The system of claim 16, wherein the mass of the two or moreheatsinks of the switching component having two or more semiconductorswitches is less than the mass of a heatsink of the switching componenthaving just one semiconductor switch on one heatsink for the sameelectrical load.